Plate heat exchangers, PHEs, typically consist of two end plates in between which a number of heat transfer plates are arranged in an aligned manner. In one type of well-known PHEs, the so called gasketed PHEs, gaskets are arranged between the heat transfer plates. The end plates, and therefore the heat transfer plates, are pressed towards each other whereby the gaskets seal between the heat transfer plates. The gaskets define parallel flow channels between the heat transfer plates through which channels two fluids of initially different temperatures alternately can flow for transferring heat from one fluid to the other. Typically, the gaskets are made of a resilient material, such as rubber.
Arranged inside a PHE, the gaskets are subjected to a number of different outer conditions that may affect the gasket material and gradually impair the gasket pressure and thus the sealing capacity of the gaskets. For example, the gaskets may be subjected to oxygen, more or less aggressive chemicals, relatively high as well as low temperatures, and compression forces. Also, time may affect the sealing capacity of the gaskets negatively. As the sealing capacity of the gaskets deteriorates, the risk of leaking flow channels increases. Therefore, the gaskets of the PHE should be replaced occasionally. It is important to know when it is suitable to replace the gaskets. Naturally, it is desirable to use the gaskets as long as possible but not for so long that a flow channel leakage arise.
From U.S. Pat. No. 7,857,036 a method and a device for assessing and detecting the risk of fluid leakage in a heat exchanger due to worn-out gaskets are known. Herein, a sensor is situated on one of the heat transfer plates, under the associated gasket which defines a fluid channel between said heat transfer plate and an adjacent heat transfer plate. The sensor monitors the pressure between said heat transfer plate and the gasket. Further, another sensor is located along the flow path of the fluid to the heat exchanger and it monitors the pressure of the incoming fluid. The pressures measures by the two sensors are used to assess the risk of leakage in the heat exchanger. However, the presence of a sensor under the gasket may have an effect on the gasket and its sealing capacity.